The main procedure for the manufacture of derivatives of benzoic acid is based on the liquid phase oxidation with air or oxygen of derivatives of toluene in the presence of metallic catalyst(s). Among the most important derivatives of benzoic acid the following can be mentioned: ortho-and para halobenzoic acids, p-methoxybenzoic ,acid (p-anisic acid), p-phenyl benzoic acid, ortho-and para toluic acids, para-nitrobenzoic acid etc.
Catalysts which were found suitable for this oxidation are generally selected from salts of metals having variable valency such as chromium, cobalt, manganese, lead, iron, copper, nickel and vanadium. Also various compounds of cerium, selenium, silver, zinc and uranium were suggested.
In addition to the catalyst(s) sometimes a promoter is utilized generally being a bromine-affording substance such as elemental, or inorganic form. Typical examples of such promoters are sodium bromide, potassium bromide, ammonium bromide, manganese bromide or the like. The literature is quite abundant with various patents on processes for the manufacture of derivatives of benzoic acid.
According to U.K. Patent Number 1,005,315 (assigned to SNIA VISCOSA), para-toluic acid is obtained by the oxidation of para-xylene with an oxygen-containing gas in the presence of a special form of cobalt oxide catalyst containing 25-35% of oxygen. The catalyst is prepared by heating a cobalt salt or oxide in the dry state at temperatures in the range of 200.degree.-800.degree. C. About 60% of the xylene was converted to p-toluic acid.
According to U.S. Pat. No. 4,007,223, p-nitrobenzoic acid is obtained by the oxidation of p-nitrotoluene with oxygen in an acetic acid reaction medium in the presence of a cobalt salt and a brominous compound (e.g.KBr, NaBr, and NH.sub.4 Br) as catalysts, the amount of acetic acid being in the range of 3 to 15 moles per mole of p-nitrotoluene. It is claimed that in this manner a not discoloured p-nitrobenzoic acid is obtained at a conversion of 92-93% of the calculated product. Other related patents dealing with the subject of p-nitrobenzoic acid are U.S. Pat. Nos. 2,883,816 and 3,665,030.
In a theoretical review "Liquid-phase oxidation of deactivated methylbenzene by aqueous sodium hypochlorite catalyzed by ruthenium salts under phase transfer catalytic conditions" (Journal of Organic Chemistry, 1986, 51, 2880), there are presented some kinetic studies on the reaction in the presence of tetrabutyl ammonium bromide. Of course, the use of an aqueous solution of sodium hypochlorite as an oxidizing reagent is of little value from an industrial point of view.
It is an object of the present invention to provide a simple process for the manufacture of derivatives of benzoic acid and salts thereof from toluene derivatives. It is another object of the present invention to provide a simple process for the manufacture of derivatives of benzoic acid and salts thereof at high yield. It is yet another object of the present invention to provide a simple process for the manufacture of derivatives of benzoic acid of a high purity.